Radio Frequency (RF) devices are quite popular in many ubiquitous applications such as Radio Frequency Identification (RFID) systems and remote sensing. For example, RFID systems consist of a number of radio frequency tags or transponders (RFID tags) and one or more radio frequency readers or interrogators (RFID readers). The RFID tags typically include an integrated circuit (IC) chip, such as a complementary metal oxide semiconductor (CMOS) chip, and an antenna connected thereto for allowing the RFID tag to communicate with an RFID reader over an air interface by way of RF signals. In a typical RFID system, one or more RFID readers query the RFID tags for information stored on them, which can be, for example, identification numbers, user written data, or sensed data. RFID systems have thus been applied in many application areas to track, monitor, and manage items as they move between physical locations.
In many of these applications, it would be convenient and beneficial if the RF energy would go to a boundary and stop, as in the situation where a wire is used to electronically transmit information. Such a boundary is one advantage of a wire. There is, however, little hope of a sharp boundary with RF energy transmitted in space. Alternatively, it would be useful in, for example, the above described application, if the data transmitted in the form of RF energy were to stop at a fixed boundary or “appear” at a fixed point while the RF energy may continue off into space as noise. For example, it would be convenient to read an RFID tag in a shopping cart in one aisle while not reading any tags from a cart in a neighboring aisle(s). In other words, if RF energy in general cannot be constrained to a boundary, it would still be beneficial to be able to constrain the data that is being transmitted using the RF energy to the desired boundary(ies).